I have had the fitbit inspire hr for a few weeks now and so far everything has worked and I was able to connect it to my mobile phone (Huawei p20 pro). However, the messages no longer load for 2 days. So I don't get WhatsApp messages or anything else on my fitbit. Reboot and reinstall the app did not work. Maybe someone has the same problem or knows how to solve it.
Make sure the Fitbit app and watch itself are up to date with the latest software / firmware.
There could also be settings for the notifications in the Fitbit app, otherwise it would be the "App notifications" item that you would have to check again.
If all else fails, I would reset the clock or set it up again.
I've given up on my Versa Lite and Huawei Mate 10 Lite. I can see calls on the watch. WhatsApp messages unfortunately not. Always works for a short time. I would recommend contacting Fitbit support, asking your question in the Fitbit forum or doing research. I always got good help with that.
Thanks then I'll try it out.